Fix build and installation of CIL library (#158)

Thanks to Zachary Anderson for the report.
Prepare for release
Install missing library file cil.a
Fix gcc machine-independent flags in cilly

Thanks to Charlie Shepherd and Stefan Hajnoczi
for the report.
Really fix machine-independent flags

The problem was not the parsing, but the fact that they need to
be passed to the preprocessor, because they might define some
macros to indicate they have been activated.
Improve README
Change version number to 1.7.3
Update changelog
Move changelog to file CHANGES